RETINOIC ACID IS A NEGATIVE REGULATOR OF THE EPSTEIN-BARR-VIRUS PROTEIN (BZLF1) THAT MEDIATES DISRUPTION OF LATENT INFECTION

Disruption of latent Epstein-Barr virus (EBV) infection is induced by the key immediate-early protein BZLF1 (or Z, a member of the basic leucine-zipper family), which transactivates the viral early promoters. Viral reactivation is marked by renewed synthesis of early gene products such as EBV early antigen-diffuse (EA-D). Retinoic acid has been previously shown to inhibit reactivation of EBV infection. Retinoic acid responsive receptors are known to act as positively regulating transcription factors but can also negatively regulate AP-1 responsive genes. Here we demonstrate that the retinoic acid receptor alpha (RARalpha) and retinoid X receptor alpha (RXRalpha) inhibit the ability of the Z protein to transactivate the viral early promoter BMRF1, which directs transcription of EA-D. Z can also reciprocally inhibit RARalpha- and RXRalpha-induced activation of an autoregulated cellular promoter for the RARbeta gene (BRE) through a non-DNA binding mechanism. RXRalpha inhibits Z from binding to the AP-1 motif in the BMRF1 promoter and, reciprocally, Z inhibits RARalpha from binding to its retinoic acid response element in the BRE promoter. Furthermore, a glutathione-S-transferase-RXRalpha fusion protein can interact directly with the Z protein. These results suggest that a direct protein-protein interaction between Z (the viral protein) and RARalpha and RXRalpha (cellular proteins) can modulate the reactivation of latent EBV infection.